insite

bull. if you were a mechanical engineer (and i am a real one), you would know that you can multiply WHEEL TORQUE with crankshaft RPMS. more power at the crank equals more possible force at the wheels. you can apply torque or force without moving anything. since we're interested in actually moving the car, we're interested in power, which is work / time.

newton's law applies to objects in motion (F=ma). it's possible, however, to apply a force without moving an object. in gross terms, if we want to move a 1000 lb car one foot, then we need to do 1000 lb-ft of work. the rate at which we do that work determines power.

mark kibort

This is correct. rate of change of kinetic energy is power! When you go back and then see the speeds, speed changes and mass, you then can pull out things like torque (or force). RPM without torque is meaningless. torque without rpms is meaningles. As i mentioned, folks get confused (even engineers, and i speak with many of them, often) with the ole, F=ma. the "F" we are talking about is that at the rear wheels. (or a=F/m) This is determined by power. Power or application of power over a period of time, is what determines acceleration.
force is a component and is what does the pushing, but it this is looked for at the rear wheels. Power will dictate/determine this.

Think HP-seconds. That can apply the most hp-seconds will win the race. He who has a flat engine torque curve of 10,000ft-lbs peak, but only 300hp, may as well be an earth moving tractor. AND, even if we could take this engine and reduce its weight to put in a R10 audi, it would still have the accelerative potential of only 300hp! why??

acceleration = power/(mass x velocity)

Once again, this means acceleration is DIRECTLY proportional to power, and inversely proportional to speed if power can be kepted relatively constant (i.e. close ratio gears)


mk

mark kibort

Acceleraton = power/(mass x velocity)

for a given mass and at any comparitive speed, acceleration is directly proportioal to power (and yes, you are part right, force or torque, but as seen by the rear tires, through the transmission)

power is not an outcome of Force x speed, its what creates it! you have it backward. power dictates force and speed, or torque/rpm.
if there is a force and no movement, you just have a force. if you have a net force, then you have movement and the distance some mass is moved is work. now, how fast you want to move it (i.e. acceleration ) is the rate of doing work, or POWER! If you dig a little deeper, you see that the energy produced by the combustion process creates the force applied to the piston face over a distance over a period of time. This is why a R10 with 650hp and 820ft-lbs of torque would have the acceleration potential equal to that of any other 650hp engine in the same car, even one that had revs to 20,000rpm and only 170ft-lbs of torque! (as long as the hp curves were the same shape and gears were spaced the same)

If you are a mechanical engineer, this is more than basic for you. (maybe too basic, as it seems it is, when this topic is discussed with engineers)

I suppose the main reason that the diesel cant rev up to say 10,000rpms is that beyond the combustion limitations, there are material limitations of the components of the engine. heavier pistons and longer strokes might be a few of the limiting components that are already strengthened in the R10's 5000rpm engine!

Mk

krC2S

yes and i am a fake one

I SAID POWER= FORCE X SPEED and that's the same as torque x angular speed so what's your point?

I SAID FORCE IS WHAT CAUSES OBJECTS TO MOVE NOT that a force applied has to cause an object to move..if for instance the force/torque applied is not enough to overcome friction then ofcourse it will not move

you can think of things in terms power if you wish but can you generate mechnaical power without any forces/torques? NO

so power is an outcome of torque/force

insite

you are correct that you can't generate power without force. you can't generate motion, though, without power. what we're saying is that flywheel POWER, not force or torque, is what determines ultimate force at the tire contact patches. you can't speak of force or torque at the flywheel and ascertain force at the wheels. you need to know the RPM and hence the power to derive that. it's not that i'm 'choosing to think about power if i want', it's that in order to determine force at the wheels, you MUST know power at the flywheel.

power at the flywheel is manipulated by the transmission into force, and ultimately power, at the drive wheels.

i'll modify your last statement. you said "power is an outcome of torque / force". i will say that torque / force at the drive wheels is an outcome of power at the flywheel coupled with torque multiplication from the transmission.

krC2S

we are not talking about converting thermal energy from combustion to mechanical energy or power.. the mechnical force generated by the combustion is what leads to motion and then mechncial power= angular speed x torque ...mechanical power is what we are discussing

the argument about the cars with sam HP and different torque just makes my point since you can't have the same HP curves unless you have the same torque curves! i.e. torque values at the same speeds

Hp curve is just the torque curve times the angular speed

yes this is basic ..nothing wrong with not knowing it if you are not an engineer
it's just amusing to see people argue strongly with wrong information!

krC2S

that's just a transmission of power or torque from one place to the other

torque at the flywheel yields power at the flywheel

and then that's transmitted to the drive wheels


Why do you have to look at crank power to get the torque at the wheels?

just use flywheel torque times your effective gear ratio ( e.g. 0.9 for 10% losses) to get drive wheel torque and the same for converting power from flywheel to crank

Mike Murphy

krC2S, insite, and mark kibort - repeat after me:

"It is better to make torque at a higher RPM than a lower RPM so we can take advantage of gearing."

That's all that needs to be said about Power vs. Torque.

insite

brain fart; i concede that point. i think we're trying to describe the same things in completely different ways.

murphyslaw - none of us can argue with that. :-)

krC2S

yes murphyslaw but i want more torque everywhere

Mike Murphy

Exactly. I'm proposing a diesel engine that can run from 1000RPM up to 7000RPM, which would have the torque curve of the Porsche 911 Turbo 997: flat as can be.

mark kibort

It all starts with power. power gives you the torque at an RPM. of course, if you wish to ignor my chicken and egg comment, then yes, you can calculate power from torque and rpm. I think we are fine there.

HOWEVER, you can have the same power curves, and im talking shape curve, i was never talking identical curve values with respect with RPM, because what point would that make?

So, you can have identical shaped HP curves, however, one can have a max rpm of say 12,000rpm and the other 6000rpm. both could have the same peak HP at 90% of the max rpm and max peak torque at 75% of their max rpm, yet one would have HALF the torque of the other at any point. Now, understanding this is a breakthrough from the common misconceptions of HP and torque. Hp is made from torque and RPM. torque is one factor of HP of equal weight with RPM. yes, force will determine HP if all you know is the force or torque and the rpm or speed. however, this misses the point of the discussion. an available HP will dictate the force at the rear tires, and unless you are looking at torques or forces acting on the car, at the rear whees, torque is a meaningless value.

two cars with identical shapped HP curves will produce the same rear wheel torque and forces at any speed, hence the newtonian identiy:
acceleration= power/(mass x velocity)

Lets say that its impossible to have the same "shaped" HP curve. Fine, thats what close ratio gear boxes allow you to do. as long as you keep the average hp, or area under the HP curves the same (comparing two totaly different engines, with different peak torque values, but equivilant HPs), you will have two cars producing the same forces at the rear wheels at any vehicle speed.
the CV joints will be experiencing the same forces. Now, up a few stages in the gear box, suddenly, the high torque engine requires greater strength gears, clutches, cranks, etc. you get the idea.

so, your point of not being able to have the same shaped HP curves without having the same torque curves is wrong. again, it would make no sense to talk about two cars with the same HP curve, as they would have the same torque curve, and that is far from what we are discussing here. (ie Diesel vs gas engine comparisons)

so, find one even tiny error in what i have posted since you are "amused" with people arguing with "wrong information" Its all very factual, and pretty basic stuff.

bottomline: acceleration = power/(mass x velocity) this means acceleration is proportioal to power and inversely proportional to speed. can you find any error in this.
also, as far as power, do you not agree that it is HP-seconds that will determine the fastest rates of acceleration. If so, and you wanted to equate this to torque (or force) you need a lot more information, as after all,
Force x distance is work
and Power is a rate of doing work. what we are really talking about with acceleration of our cars, is the difference of the rate of doing work.

to prove my points, one example that you can try and argue or explain.

two cars, as mentioned above. both 700hp, but one with 300ft-lbs of peak torque and the other with 600ft-lbs of peak torque. assuming the same car, weight, proportional gear boxes and same shaped HP curve.
coming off a 40mph turn approaching a 1/2mile straight , which one would have an advange and why?


MK

mark kibort

murphyslaw, can i translate your regurgetation of bruce augustines mistake riddled hp vs torque website?

ok, i will anyway. Translation is this: It is better to make more hp than less hp.

More torque at a higher rpm will yield more HP. and yes, since we have proved that HP dictates the torque through the gear box at the driven wheels, this statement is true. more hp is what we want (or what i want if i want to win races) , and i could care less if it happens with high torque at low rpms or low torque at high rpms. HP will dictate the accelerative forces at the rear tires. The only difference will be what it sounds like.

Gearing doesnt make HP, it only makes more efficient use of the HP that is available . Thats another discussion as well.


Mk

mark kibort

another misnomer. even the R10 doesnt have a "flat" torque curve in its usuable range. its 820 ft-lbs falls dramatically as it approaches 5000rpm as it has to otherwise it would have a heck of a lot more power than 650!!

the 911 turbo, has a flat HP curve, not a flat torque curve (in the useable racing range) all torque curves fall, its just a matter of by how much.

what we all want is a flat HP curve, this means torque is only falling at a 45 degree angle! when the torque curve is flat, it means Hp is climbing at a 45 degree angle.

Here is a good comparison of two very different engines , one being a V8 and the other an I6. both have near the same rwhp. the shapes of the curves are remarkably the same, yet, one has 300ftlbs of torque and the other 225ft-lbs of torque. both will accelerate at the exact same rate at any speed. (as long as the gear spacing is the same and actualy with these two cars , they are pretty close in that area)

the first graph is a pretty stout 911 turbo with 3 different graphs based on higher and higher boost levels. 1.0bar, 1.1bar and 1.2bar (fyi of what the curves , both hp and torque look like)

mk

mark kibort

krC2S, I think what "Insite" was trying to make as a point, was that power determines torque at the rear wheels at any speed. Sure, you can always go multiplying to your hearts content, to figure out what torque you have at the rear wheels through any gear box ratio at any speed. however, if you now are looking at accelerative forces at differnt speeds, it becomes much easier to look at the power comparisons. Engine torques also have to be coupled with rpm (ie HP) to get a final drive torque at the rear wheels at any vehicle speed through the gear box. more steps for a comparison. however looking at a HP curve, i can tell you which vehicle will win a race over a speed range by only knowing gear spacing. Its just easier and you need less information because more is included in HP. remember, its made up of torque and rpm.

mk